Few predicted that the constitutional fate of the Patient Protection and Affordable Care Act would turn on Congress’ power to lay taxes. Yet in NFIB v. Sebelius, the Supreme Court upheld the centerpiece of the Act — the minimum coverage provision (MCP), commonly known as the “individual mandate” — as a tax. The surprising constitutional basis of the Court’s holding has deflected attention from what may prove to be the decision’s more constitutionally meaningful feature: that a majority of the Court agreed that Congress lacked authority under the Commerce Clause to penalize individuals who decline to purchase health insurance. Chief Justice Roberts and the four joint dissenters endorsed the novel limiting principle advanced by the Act’s challengers, distinguishing between economic “activity,” which Congress can regulate, and “inactivity,” which it cannot. Because the commerce power extends only to “existing commercial activity,” and because the uninsured were “inactive” in the market for health care, they reasoned, Congress lacked authority under the Commerce Clause to enact the MCP. Critically, supporters of the activity/inactivity distinction insisted that it was an intrinsic constraint on congressional authority anchored in the text of Article I and the structural principle of federalism, rather than an “affirmative” prohibition rooted in a constitutional liberty interest.

This Article argues that the neat dichotomy drawn by the Chief Justice and joint dissenters’ between intrinsic and rights-based constraints on legislative authority is false, and that it obscures both the underlying logic and broader implications of the activity/inactivity distinction as a constraint on congressional authority. In fact, that distinction is animated less by the constitutional enumeration of powers or federalism than a concern about individual liberty. Even in the absence of a formal constitutional “right” to serve as a doctrinal vehicle, the justices’ defense of economic liberty operates analogously to the substantive due process right to “liberty of contract” during the Lochner era — as a trigger for heightened scrutiny of legislative means and ends — through which the justices constricted the scope of the commerce power.

Current scholarship addressing the role of individual liberty in NFIB v. Sebelius tends to deploy Lochner as a convenient rhetorical touchstone, to lend an air of illicitness or subterfuge to the majority’s Commerce Clause analysis. I argue that the Lochner-era substantive due process cases are both more nuanced and more instructive than judges and many scholars have realized. They illustrate, in particular, that constraints on legislative authority that are rooted in individual liberty and constraints on legislative authority that are rooted in enumerated powers and federalism can and do operate in dynamic relationship to one another. Reading NFIB v. Sebelius through this historical lens better equips us to interrogate the role that economic liberty plays in the majority’s Commerce Clause analysis, and provides an important alternative analytical framework to the structure/rights dichotomy advanced by the Chief Justice and joint dissenters. The activity/inactivity distinction not only portends a constitutionally dim future for federal purchase mandates, but may also herald more far-reaching restrictions on congressional interference with individual liberty, in which individual sovereignty assumes a place alongside state sovereignty in the Court’s federalism.